How to change Chain Lenght in Inverse Kinematics?
You can tell from the yellow dotted line that runs from the IK bone (the yellow one) that there is indeed a difference in the IK chain length (the dotted line runs to a different bone for each leg). If you go to the IK constraint options, there is an option for chain length. Make sure that this option is set to the same number for both legs (it looks like it should be set to 2). Leaving it at the default value of 0 will give a limitless chain, and any number over 2 will include the hip bone, both of which will cause the problems you are seeing.

This is the value you will need to change: